In recent years, reduction of carbon dioxide emission amount is eagerly desired in order to cope with the atmospheric pollution and the global warming. In the car industry, reduction of carbon dioxide emission amount by introduction of an electric car (EV), a hybrid electric car (HEV) or the like draws attention, and development of an electrical device such as a secondary battery for driving a motor, which is a key to practical application of them, is actively carried out.
As a secondary battery for driving a motor, a lithium ion secondary battery having high theoretical energy attracts attention, and development thereof is currently underway rapidly. A lithium ion secondary battery is generally constituted such that a positive electrode formed by applying a slurry for positive electrode containing a positive electrode active material onto the surface of a current collector, a negative electrode formed by applying a slurry for negative electrode containing a negative electrode active material onto the surface of a negative electrode current collector, and an electrolyte located between them, are accommodated in a battery case.
Selection of each active material is very important in order to improve capacity property, output property, and the like of a lithium ion secondary battery.
In the past, a cathode composition for a lithium ion battery having a formula (a) Liy[M1(1-b)Mnb]O2 or (b) Lix[M1(1-b)Mnb]O1.5+c (in the formula, 0≤y<1, 0<b<1, and 0<c<0.5, and M1 represents one or more metal elements; however, in the case of (a), M1 is a metal element except for chromium), was suggested, wherein the cathode composition for a lithium ion battery is in a form of single phase having O3 crystal structure that does not cause phase transition to spinel crystal structure when the cathode composition for lithium ion battery is incorporated into a lithium ion battery, and cycle operations of 100 complete charge-discharge cycles are performed at 30° C. and 130 mAh/g of the final capacity using 30 mA/g of the discharge current (see Japanese Patent No. 2004-538610).
However, during investigation of the inventors, there has been a problem that the lithium ion battery using a cathode composition for a lithium ion battery described in Japanese Patent No. 2004-538610 cannot realize high discharge capacity and capacity retention rate.